The oil and gas industry uses various methods to test the productivity of wells prior to completing a well (see, for example, U.S. Pat. No. 4,898,236). After drilling operations have been completed and a well has been drilled to total depth, or prior to reaching total depth in the case of multi-zoned discoveries, it is common to test the zone to estimate future production of oil and gas. Current technologies used for testing reservoirs such as drill stem testing (DST) are often too expensive to test multi-zone reservoirs, particularly at shallow depths. Furthermore, isolating and testing zones using conventional packer technology can be slow, expensive and sometimes difficult to set and then release.
Traditionally the DST process involves flowing a well through a length of drill pipe reinserted through the static drilling fluid. The bottom of the pipe will attach to a tool or device with openings through which fluid can enter. This perforated section is placed across an anticipated producing section of the formation and sealed off with packers, frequently a pair of packers placed above and below the part of the formation being tested. This packing off technique permits an operator to test only an isolated section or cumulative section.
The present invention allows a fast, safe and economic way to isolate and test zones during reverse circulation drilling by using the already inserted concentric drill string used during drilling. This alleviates the need to first remove the drill string used for drilling and then reinsert a length of drill pipe or coiled tubing for testing.